In compact film cameras and digital still cameras equipped with an image-pickup element such as a CCD sensor, a so-called collapsible lens apparatus is provided for good portability, which is housed in the camera body in a non-image-taking state.
In such a collapsible lens barrel, a barrel member is movable in a direction of the optical axis by the engagement of a cam groove portion and a cam follower pin.
When the lens barrel is in a protruded state (image-taking state), there is a possibility that the front barrel will receive a strong impact in a case where the camera is dropped or collides with something in a state in which the camera is hung with a strap. Therefore, a lens barrel has been disclosed in Japanese Patent Laid-Open application 2002-90611, which has a structure capable of preventing the disengagement of the cam groove portion and cam follower pin.
In the lens barrel disclosed in Japanese Patent Laid-Open application 2002-90611, the disengagement of a tapered roller for cam driving from the cam groove portion is prevented by the contact of a cylindrical roller, which is provided separately from the tapered roller, with a disengagement preventing groove portion.
However, in the lens barrel disclosed in Japanese Patent Laid-Open application 2002-90611, the tapered roller and the cylindrical roller are arranged in the optical axis direction. In this case, when an external force acts on the lens barrel, the lens barrel is deformed, and thereby the tapered roller is displaced along the sidewall of the cam groove portion and the cylindrical roller is also displaced. Consequently, the contact area of the cylindrical roller and the disengagement preventing groove portion is reduced. This is not preferable for ensuring the strength of the lens barrel.